The present invention relates to a slot antenna, and in particular to a slot antenna mounted in a portable electronic device and operating in the ISM (Industry, Science, Medicine) frequency band for communicating with various external electronic devices.
There is a growing need for slot antennas for use in wireless communication devices such as notebook computers, Bluetooth apparatus, IEEE802.11 apparatus, wireless LANs, 2.4xcx9c2.5GHz apparatus, and in other applications. Commonly, a slot is formed in a conductive sheet, which is then used as a radiating or receiving element in an antenna. Slot antennas formed with flat metal foil are widely used.
FIG. 13 shows a conventional antenna assembly. A flat slot antenna 14 is made from a metal foil 10 having dimensions 68 mm xc3x9711 mm, and has an elongated narrow slot 12 with dimensions 55 mm xc3x970.7 mm defined therein. A cable 13 has an inner core wire soldered to a flat surface 11 at a first feed-in point 132 near the slot 12, and an outer shield soldered to the flat surface 11 at a second feed-in point 131 near the slot 12 and opposite the first feed-in point 132. Each feed-in point 131, 132 is 4 mm away from an end of the slot 12.
FIG. 14 shows a measured radiation pattern of the flat slot antenna 14 of FIG. 13 in the X-Z plane. Radiation voids were present at angles 90xc2x0 and 270xc2x0 in the X-Z plane. In other words, the X-Z plane has low directivity. Furthermore, a resonant current of the slot in the X-Z plane is small. A measured electric field intensity of the X-Z plane is less than the electric field intensity of the X-Y plane and the Y-Z plane. Thus the radiation in the X-Z plane is weak. The flat slot antenna 14 does not achieve omni-directional radiation.
FIG. 15 shows a table of total average gains of the flat slot antenna 14 in the X-Y plane, the Y-Z plane and the X-Z plane at different frequencies when a conventional notebook computer is open.
As seen in FIG. 15, the average gain of the flat slot antenna 14 in the X-Z plane is 4xcx9c5 dB less than the average gain in the X-Y plane, and 2xcx9c3 dB less than in the Y-Z plane.
A notebook computer with an antenna mounted therein may be used in a variety of different locations. Each location has a different environment which can affect the proper functioning of the antenna. Thus the radiation electric field intensity of the antenna should be sufficiently large and omni-directional to allow the notebook to operate properly in various environments.
Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of existing wireless network equipment.
Therefore, a primary object of the present invention is to provide an antenna assembly having omni-directional radiation.
Another object of the present invention is to provide an antenna assembly having an arcuate shape for increasing effective radiation.
A further object of the present invention is to provide an antenna assembly occupying minimal space within an electronic device.
An antenna assembly in accordance with the present invention comprises an arcuate slot antenna and a coaxial feeder cable. The slot antenna comprises a metal foil which is bent diagonally to form an arcuate surface. The slot antenna defines an elongated narrow slot therein. An inner core of the cable is soldered to the arcuate surface at a first feed-in point near an end of the slot. An outer shield of the cable is soldered to the arcuate surface at a second feed-in point near the end of the slot and opposite the first feed-in point.
The slot antenna has a superior scope of maximum directive gain, and a superior total average gain in the X-Y plane, the Y-Z plane and the X-Z plane.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of a preferred embodiment when taken in conjunction with the accompanying drawings.